Vehicle manufacturers are developing hybrid vehicles to meet the demand for more fuel efficient vehicles. One configuration for a hybrid vehicle can be referred to as a Modular Hybrid Transmission (MHT) vehicle design. In a so-called MHT vehicle, an electric machine is sandwiched between a conventional automatic step ratio transmission and an engine. The electric machine is attached to the transmission impeller or input shaft. The engine is selectively disconnected from the transmission using a disconnect clutch. The disconnect clutch allows the vehicle to be driven under electric power alone, in hybrid mode with both electric machine and the engine propelling the vehicle, or in a combustion engine only mode in which the vehicle is propelled by the engine only.
As hybrid vehicles have been developed to utilize both an engine and a motor to drive a vehicle transmission, most hybrid systems interact with the transmission through clutches between the drive sources and the transmission. The controls for the various clutches between the sources and within the transmission have complicated the control mechanism, and can reduce efficiency and driveability as the clutches engage and disengage during power distribution adjustment in the driveling.